Squirrel-cage winding for alternating-current motors



Sept. 9. 1924,

P. L. ALGER SQUIRREL CAGE WINDING FOR ALTERNATING CURREN T MOTORS FiledMay 4, 1922 Lager;

Patented Sept. 9, 1924.

PATENT OFFlfiE.

PHILIP L ALGER, 0F SGHENECTADY, NEW YORK, ASSIGNOB T0 GENERAL ELECTRIC.

- without psnying drawings in which COMPANY, A CORPORATION OF NEW YORK.

SQUI'RBEL -GAGE WINDING FOR ALTER NATING-CURBENT KOTOBB.

Application filed Kay 4,

To oZZ whom c't concern;

Be it known that I, PHILIP L. y citizen or" the United States, residingin Schenectady, county of Schenectady, State of New York, have inventedcertain new and useful Improvements in Squirrel-Cage Windings forAlternating-Current Motors, of which the following is a specification.

y invention relates to alternating cur rent motors and more particularlyto altermating motors provided with one or-more squirrelcnge windings ontheir rotor elements.

Various 'expedients have been resorted to in the construction ofsquirrel cage rotors both in the synchronous and asynchronous types ofmotorswith a view of obtaining the most desirable starting and operatingcharacteristics. These characteristics have been obtained in manyinstances by sacrificing or regard to the most desirable mechanicalconstruction. It is the object of my invention to improve the mechanicalconstruction of the rotor element of such motors without sacrificing toany extent the desirable starting and operating characteristics found incurrent motors. The improvementsin 1nechanical design contemplated bythe present a plication include the simplest possible mecl ianicalconstruction whic will permit of a wide variation in the electricalconstants of the squirrel cage with a slot of standard dimensions. 5 j

The features of my invention which I believe to be novel and patentablewill be pointed out in thoc'lairns appended hereto. The details ofconstruction thereof will now be explained in connection with the accom-Figs. 1 and 2 squirrel cage Amen, 2

represent cross sections 'of structures more particularly adapted forsynchronous motors. Fig. 3 illustrates a cross section of a doublesquirrel cage induction motor rotor; Figs. 4 and 6 represent sectionstaken on the slot edge of 1 and 3, respectively, showing the end ringstructure. and Figs. 5 and 7 represent end views of Figs. 4 and 6.-respectively.

Referring now more in particular to Figs. 1, 2, 4 and 5', 1 representrectangulrir squirrel cage bars placed in the. bottom of straight edgerectangular slots 2 punched in the laminations 3 and having overhangingretaining portions at the periphery thereof. The

commercial alternating 1922. ,sernu 1T0. 558,408.

lends itself towide variations in the elecsquirrel'cage is desired, Imay decrease the depth of bars 1 and increase the dept-h of bars5 andthat if a-lower resistance squirrel cage is desired, I increase thedepth of bars 1 and decreasethe de th of bars 5. I might also insulateburst lbom the squirrel cage or I might weld them together and vary [isconductance of the squirrel cage in this mztnncrr- Furthermore, thereactance of the squirrel cage may be variediivhile using the same sizeslots by varying th'width 'oi-the magnetic bridge formed by bars 5. Thusin Fig. 2T1. lave decreased the width of bar 5 and filled up theremaining space by a wedge 6 of any sultable material such as copper orhorn fibre. It will be evident that the wedge 6 will be retained inplace ust radial and endwise movements in the ...urne manner asdescribed in connection.with bars 5.. The width of the bridge may bestill further decreased by providing an additional wed e on the otherside of the slot shown in Fig. 2. Furthermore, the reactance might bechanged without changing the width of the slots or the resistance (ifthe squirrel cage by decreasing the depth of. the magnetic bridges abovethe squlrrel cage and inserting similar but narrower bars beneath thesquirrel cage. It will be evident from an inspection of Figs. t and 5that all such bars and wedges will be prevented from endwiso movementsby the end rings 4. Again, the electrical characteristics of thesquirrel cage winding may be varied to some extent by making the bridges5 and wedges 6 of diiferent materials. With a magnetic bridge 5 and acopper wedge 6 c certain amount of K eddy currents will he producedtherein; The eddy currentsniay be varied by varying the conductivity ofthe members i and :3. Thus, i might laminate the magnetic bridge 1 incdirection to decrease eddy currents without verying he reaclauce. of theuiulensionsof the parts. shown in Figs. 31, 2,, 4 and 5 are particularlydesigned for obtaining the most desirable compromise between thestarting torque, pull-in torque and mechanical characteristics in asynchronous motor provided with a squirrel cage Winding. Such .n.rriotor svould be provided. with fixed polar projections having directcurrent field. windings thereon With u squirrel cage winding in theperiphery of the projections. Figs. 1, 2, 3 and i may represent sectionsof the periphery oi such a rotor. The characteristics of a synchronousmotor provided with the squirrel cage structure of Fig. 2 will he asfollows: At starting, line frczpiency currents flow. in the squirrelwindingnuihing a line frequency flux across the slots through bars 5 endWedges 6. As the bars 5 are made of solid metal, circulating currentswill he set up therein which will flow across the top of the bars andback along the hottom. in such a. way as to oppose the passage of theflux. These currents will n'iake losses which will produce torquejusltruly as the actual copper losses in the squirrel cage Winding producestorque. Thus the cfl ect Without the disadvantage of pole cm losses atfull speed ordinarily incurred by solid pole construction. At full speedthe currents in the squirrel cage winding are small and of low frequencyand consequently the flux will no longer cross the magnetic bridgeformed by bars 5 but will flow down through the pole in the usual way.Thus. relatively low resistance running and high resistance astarting'characteristics of the squirrel cage are obtained. The current carryingconduc tors oi the squirrel cage Winding are not subjected to excessiveheating because the losses at starting occur almost entirely in thesteel hers 5. The cll'ect of a. minimum depth of slotis obtained becauseall the space above the current carrying conductors is utilized forcarrying flux. whereas in a double squirrel cage construction a part ofhe vuluuhle space in the top of the slot is d for carrying a high.resistance her of considerable depth. it will. thus be evident that suchat construction has the desirable characteristics of the usual doublesquirrel cage Winding. In the construction of squirrel cage Windings'ofsynchronous motors itis an advantage to make the resistance of thesquirrel cage bars lying in the central po'rtiouot the pole piece lessthan the resistuse of a solid steel pole is secured ahsturting once ofthose bars at the edges of the pole pieces. In the form of winding abovede scribed this desirable feature may be readily obtained Without thenecessity of using dif' fercnt size slots.

Although the rectangular slot and her construction is the more desirablefrom the point of -view of mechanical construction, the shape of thehers is immaterial in so faras the electrical characteristics of themotor are concerned, and it will therefore he evident that the lastmentioned aspect ol my invention is not limited to an particular shapeof the bars or slots.

' Referring now to Figs. 3, 6 and 7, I have illustrated the mechanicalfeatures of my invention applied to an ordinary d0uble squirrel cageinduction motor rotor in which the roto'ris provided with rectangularpartially closed slots 2' containing double squirrel cage Windingconsisting of bars 1' in the bottom of the slots. bars T in the top ofthe slots and the common end rings 4. These will he made of some goodconducting material such as copper, brass or aluminum although they neednot necessarily all be made of the some materiel. Betwcenthhse windingsisv placed a solid rectangular car 5, preferably of steel, and a Wedge6. preferably of copper, r nor fibre. The parts are adapted tocompletely fill the slots and the bars 5' and Wedges 6' are preventedfrom worlrin out endivisc by plugsfl in the end rings. glrdinerily. theand rings will be provided with an opening extending the "full depth ofthe three bars 1, 5' and 7 and after the parts are assembled, thatportion 8 between the two squirrel cage bars will be filled in at thesome time the end rings are secured to the squirrel cage hers. such. forexample, as by Welding or brazing. This provides a simple, rugged,double squirrel cage structure the electrical characteristics of whichmay be readily changed Without changing theidimensions ofthe slots orend, rings. ThusQl-he relative resistances of the two squirrel cages mayhe changed by changing the relative depth of the cars l and 7. Thedesired reactance of the lower squirrel cage may he obtained by varyingthe relative width of the magnetic bridge 5 and the wedge 6. l donotconsider that the production 0? eddy currents in bars 5' will he of anyappreciahle amount or that such currents will he oi any psrti culoradvantage in a double squirrel cage structure such as illustrated in 3,6 and 7. i

It will he evident that a motor with the features hereinloeforedcscrihed will sdvantegeo'us Irom a manufacturing point of view becauseonly one size and type of rotor punchings and end rings are required forroanniecturmg motors (if/different charm teristics, the desiredcharacteristics being ob,- tained by changing the dimensions andarrangement ot the bars placed in the slots.

In accordance with the provisions of the patent statutes, I havedescribed the principle of operation of my invention, together with theapparatus which I now consider to represent the best embodiment thereof:but I desire to have it understood that the apparatus shown is onlyillustrative and that the invention may be carried out in various ways.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. An alternating current motor rotor provided with rectangular slots inthe peripheral portions thereof, a squirrel cage winding comprisingrectangular bars in said slots and end rings at the extremities of saidrotor and rectangular magnetic wedges in said slots above said barsabutting against said end rings.

2. An alternating current motor rotor provided with rectangularpartially closed slots in the peripheral portions thereof, a squirrelcage winding comprising bars in said slots and end rings at theextremities of said rotor and bridges above said bars in said slotscomprising rectangular bars of magnetic and non-magnetic material, saidbridge members abutting against said end rings.

3. An alternating current motor comprising cooperating stator and rotormembers, said rotor member comprisin a cylindrical laminated coreprovided Witi rectangular partially closed slots in its periphery, apinrality of squirrel cage windings having common end rings and having;rectangular bars in each of said slots at different radial depthstherein and rectangular bars of mag uetic material between said squirrelcage bars abutting against said end rings.

i. .\n alternating current motor comprising cooperating stator and rotorelements, sai'd rotor element consisting of a cylindrical laminated corewith rectangular partially closed slots in its periphery, a doublesquirrel cage winding having bars in each of said slots and bridgesbetween said squirrel cage bars comprising rods of magnetic andnon-magnetic material of such relative dimensions as to produce thedesired flux path between said squirrel cage windings, said squirrelcage bars andbridge rods completely filling, the rectangular portionsor" said slots.

An alternating current motor comprising cooperating stator and IOtOrelements, said rotor elements comprising a laminated structure providedwith slots in its peripheral portions. a squirrel cage winding hav ingconducting bars in the bottoms of said slots and a bridge member abovesaid bars in said slots consisting of rods of magnetic and non-magneticmaterials placed side by side, the relative dimensions of said rodebeing such as to give the squirrel cage winding any desired reactancewithin the limits of the structure.

In witness whereof, I have hereunto set my hand this 3rd day of May,1922.

PHILIP L. ALGER.

